In hydrolytic copolycondensation of a silicon compound having a hydrolyzable group, acidic and alkaline conditions have a catalytic function. It has been known since old times that the condensation has different chemical mechanisms under acidic or alkaline conditions. For example Non-patent Document 1 discloses that tetraethoxysilane, which is a silicon compound of SiX4 form, is hydrolyzed by an acid or alkali catalyst, whereas monomethyltriethoxysilane of RSiX3 form causes reaction in the presence of an acid catalyst, but is unreactive in the presence of an alkali catalyst.
Patent Document 1 discloses that an acid catalyst opens the ring of an oxetanyl group, and that a method for producing a condensed silicon compound having an oxetanyl group, through the hydrolytic polycondensation of a silicon compound having an oxetanyl group and three hydrolyzable groups under an alkaline condition.
Patent Document 2 discloses that a silicon compound having an oxetanyl group and three hydrolyzable groups can be hydrolyzed and cocondensed with a reactive silicone having one or more siloxane bond-forming groups in one molecule thereof under an alkaline condition, and that the cured product of the condensate exhibits high contamination resistance owing to the effect of the silicone chain.
On the other hand, Patent Document 3 discloses a method for producing a condensed silicon compound having an oxetanyl group through the hydrolytic polycondensation of a silicon compound having an oxetanyl group and three hydrolyzable groups in the presence of an acid catalyst. The cured film of the condensed silicon compound obtained by the method showed markedly better result in a pencil hardness test in comparison with a silicone-containing cured film disclosed in Example of Patent Document 2, and thus is suitable for applications requiring surface hardness.
However, Patent Document 3 discloses that in Comparative Example 1 gelation occurred during the hydrolytic copolycondensation of a silicon compound having an oxetanyl group and three hydrolyzable groups, and a silicon compound having three siloxane bond-forming groups under an alkaline condition. It suggests that the possibility of gelation caused by the hydrolytic polycondensation of a silicon compound having an oxetanyl group and three hydrolyzable groups under an alkaline condition.
In Patent Document 3, cocondensation of a silicon compound having four siloxane bond-forming groups and a silicon compound having three hydrolyzable groups in the presence of an acid catalyst is specifically described in Example 8. The evaluation of the cured product of the silicon compound obtained by hydrolytic copolycondensation was not so different from that obtained using a silicon compound having three siloxane bond-forming groups. In summary, regarding the cocondensation of a silicon compound having an oxetanyl group and three hydrolyzable groups and a silicon compound having four siloxane bond-forming groups under an alkaline condition, there are known documents suggesting the possibility of gelation and no expectation for any special effect.